MAINTENANCE COMANDS SUDO(1m)
NAME
sudo, sudoedit - execute a command as another user
SYNOPSIS
sudo -h -K -k -L -l -V -v
sudo [-bEHPS] [-p prompt] [-u username#uid] [VAR=value]
{-i -s command}
sudoedit [-S] [-p prompt] [-u username#uid] file ...
DESCRIPTION
sudo allows a permitted user to execute a command as the
superuser or another user, as specified in the sudoers file.
The real and effective uid and gid are set to match those of
the target user as specified in the passwd file and the
group vector is initialized based on the group file (unless
the -P option was specified). If the invoking user is root
or if the target user is the same as the invoking user, no
password is required. Otherwise, sudo requires that users
authenticate themselves with a password by default (NOTE: in
the default configuration this is the user's password, not
the root password). Once a user has been authenticated, a
timestamp is updated and the user may then use sudo without
a password for a short period of time (5 minutes unless
overridden in sudoers).
When invoked as sudoedit, the -e option (described below),
is implied.
sudo determines who is an authorized user by consulting the
file /etc/sudoers. By giving sudo the -v flag, a user can
update the time stamp without running a command. The
password prompt itself will also time out if the user's
password is not entered within 5 minutes (unless overridden
via sudoers).
If a user who is not listed in the sudoers file tries to run
a command via sudo, mail is sent to the proper authorities,
as defined at configure time or in the sudoers file
(defaults to root). Note that the mail will not be sent if
an unauthorized user tries to run sudo with the -l or -v
flags. This allows users to determine for themselves
whether or not they are allowed to use sudo.
If sudo is run by root and the SUDOUSER environment
variable is set, sudo will use this value to determine who
the actual user is. This can be used by a user to log
commands through sudo even when a root shell has been
invoked. It also allows the -e flag to remain useful even
when being run via a sudo-run script or program. Note
however, that the sudoers lookup is still done for root, not
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the user specified by SUDOUSER.
sudo can log both successful and unsuccessful attempts (as
well as errors) to syslog(3), a log file, or both. By
default sudo will log via syslog(3) but this is changeable
at configure time or via the sudoers file.
OPTIONS
sudo accepts the following command line options:
-b The -b (background) option tells sudo to run the given
command in the background. Note that if you use the -b
option you cannot use shell job control to manipulate
the process.
-E The -E (preserve environment) option will override the
envreset option in sudoers(4)). It is only available
when either the matching command has the SETENV tag or
the setenv option is set in sudoers(4).
-e The -e (edit) option indicates that, instead of running
a command, the user wishes to edit one or more files.
In lieu of a command, the string "sudoedit" is used when
consulting the sudoers file. If the user is authorized
by sudoers the following steps are taken:
1. Temporary copies are made of the files to be edited
with the owner set to the invoking user.
2. The editor specified by the VISUAL or EDITOR
environment variables is run to edit the temporary
files. If neither VISUAL nor EDITOR are set, the
program listed in the editor sudoers variable is
used.
3. If they have been modified, the temporary files are
copied back to their original location and the
temporary versions are removed.
If the specified file does not exist, it will be
created. Note that unlike most commands run by sudo,
the editor is run with the invoking user's environment
unmodified. If, for some reason, sudo is unable to
update a file with its edited version, the user will
receive a warning and the edited copy will remain in a
temporary file.
-H The -H (HOME) option sets the HOME environment variable
to the homedir of the target user (root by default) as
specified in passwd(4). By default, sudo does not
modify HOME (see sethome and alwayssethome in
sudoers(4)).
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-h The -h (help) option causes sudo to print a usage
message and exit.
-i The -i (simulate initial login) option runs the shell
specified in the passwd(4) entry of the user that the
command is being run as. The command name argument
given to the shell begins with a `-' to tell the shell
to run as a login shell. sudo attempts to change to
that user's home directory before running the shell. It
also initializes the environment, leaving TERM
unchanged, setting HOME, SHEL, USER, LOGNAME, and PATH,
and unsetting all other environment variables. Note
that because the shell to use is determined before the
sudoers file is parsed, a runasdefault setting in
sudoers will specify the user to run the shell as but
will not affect which shell is actually run.
-K The -K (sure kill) option is like -k except that it
removes the user's timestamp entirely. Like -k, this
option does not require a password.
-k The -k (kill) option to sudo invalidates the user's
timestamp by setting the time on it to the Epoch. The
next time sudo is run a password will be required. This
option does not require a password and was added to
allow a user to revoke sudo permissions from a .logout
file.
-L The -L (list defaults) option will list out the
parameters that may be set in a Defaults line along with
a short description for each. This option is useful in
conjunction with grep(1).
-l The -l (list) option will list out the allowed (and
forbidden) commands for the invoking user on the current
host.
-P The -P (preserve group vector) option causes sudo to
preserve the invoking user's group vector unaltered. By
default, sudo will initialize the group vector to the
list of groups the target user is in. The real and
effective group IDs, however, are still set to match the
target user.
-p The -p (prompt) option allows you to override the
default password prompt and use a custom one. The
following percent (`%') escapes are supported:
%H expanded to the local hostname including the domain
name (on if the machine's hostname is fully
qualified or the fqdn sudoers option is set)
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%h expanded to the local hostname without the domain
name
%p expanded to the user whose password is being asked
for (respects the rootpw, targetpw and runaspw flags
in sudoers)
%U expanded to the login name of the user the command
will be run as (defaults to root)
%u expanded to the invoking user's login name
%% two consecutive % characters are collapsed into a
single % character
-S The -S (stdin) option causes sudo to read the password
from the standard input instead of the terminal device.
-s The -s (shell) option runs the shell specified by the
SHEL environment variable if it is set or the shell as
specified in passwd(4).
-u The -u (user) option causes sudo to run the specified
command as a user other than root. To specify a uid
instead of a username, use #uid. When running commands
as a uid, many shells require that the '#' be escaped
with a backslash ('\'). Note that if the targetpw
Defaults option is set (see sudoers(4)) it is not
possible to run commands with a uid not listed in the
password database.
-V The -V (version) option causes sudo to print the version
number and exit. If the invoking user is already root
the -V option will print out a list of the defaults sudo
was compiled with as well as the machine's local network
addresses.
-v If given the -v (validate) option, sudo will update the
user's timestamp, prompting for the user's password if
necessary. This extends the sudo timeout for another 5
minutes (or whatever the timeout is set to in sudoers)
but does not run a command.
-- The -- flag indicates that sudo should stop processing
command line arguments. It is most useful in
conjunction with the -s flag.
Environment variables to be set for the command may also be
passed on the command line in the form of VAR=value, e.g.
LDLIBRARYPATH=/usr/local/pkg/lib. Variables passed on the
command line are subject to the same restrictions as normal
environment variables with one important exception. If the
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setenv option is set in sudoers, the command to be run has
the SETENV tag set or the command matched is AL, the user
may set variables that would overwise be forbidden. See
sudoers(4) for more information.
RETURN VALUES
Upon successful execution of a program, the return value
from sudo will simply be the return value of the program
that was executed.
Otherwise, sudo quits with an exit value of 1 if there is a
configuration/permission problem or if sudo cannot execute
the given command. In the latter case the error string is
printed to stderr. If sudo cannot stat(2) one or more
entries in the user's PATH an error is printed on stderr.
(If the directory does not exist or if it is not really a
directory, the entry is ignored and no error is printed.)
This should not happen under normal circumstances. The most
common reason for stat(2) to return "permission denied" is
if you are running an automounter and one of the directories
in your PATH is on a machine that is currently unreachable.
SECURITY NOTES
sudo tries to be safe when executing external commands.
There are two distinct ways to deal with environment
variables. By default, the envreset sudoers option is
enabled. This causes commands to be executed with a minimal
environment containing TERM, PATH, HOME, SHEL, LOGNAME,
USER and USERNAME in addition to variables from the invoking
process permitted by the envcheck and envkeep sudoers
options. There is effectively a whitelist for environment
variables.
If, however, the envreset option is disabled in sudoers,
any variables not explicitly denied by the envcheck and
envdelete options are inherited from the invoking process.
In this case, envcheck and envdelete behave like a
blacklist. Since it is not possible to blacklist all
potentially dangerous environment variables, use of the
default envreset behavior is encouraged.
In all cases, environment variables with a value beginning
with () are removed as they could be interpreted as bash
functions. The list of environment variables that sudo
allows or denies is contained in the output of sudo -V when
run as root.
Note that the dynamic linker on most operating systems will
remove variables that can control dynamic linking from the
environment of setuid executables, including sudo.
Depending on the operating system this may include RLD*,
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DYLD*, LD*, LDR*, LIBPATH, SHLIBPATH, and others. These
type of variables are removed from the environment before
sudo even begins execution and, as such, it is not possible
for sudo to preserve them.
To prevent command spoofing, sudo checks "." and "" (both
denoting current directory) last when searching for a
command in the user's PATH (if one or both are in the PATH).
Note, however, that the actual PATH environment variable is
not modified and is passed unchanged to the program that
sudo executes.
sudo will check the ownership of its timestamp directory
(/var/run/sudo by default) and ignore the directory's
contents if it is not owned by root or if it is writable by
a user other than root. On systems that allow non-root
users to give away files via chown(2), if the timestamp
directory is located in a directory writable by anyone
(e.g., /tmp), it is possible for a user to create the
timestamp directory before sudo is run. However, because
sudo checks the ownership and mode of the directory and its
contents, the only damage that can be done is to "hide"
files by putting them in the timestamp dir. This is
unlikely to happen since once the timestamp dir is owned by
root and inaccessible by any other user, the user placing
files there would be unable to get them back out. To get
around this issue you can use a directory that is not
world-writable for the timestamps (/var/adm/sudo for
instance) or create /var/run/sudo with the appropriate owner
(root) and permissions (0700) in the system startup files.
sudo will not honor timestamps set far in the future.
Timestamps with a date greater than currenttime ] 2 *
TIMEOUT will be ignored and sudo will log and complain.
This is done to keep a user from creating his/her own
timestamp with a bogus date on systems that allow users to
give away files.
Please note that sudo will normally only log the command it
explicitly runs. If a user runs a command such as sudo su
or sudo sh, subsequent commands run from that shell will not
be logged, nor will sudo's access control affect them. The
same is true for commands that offer shell escapes
(including most editors). Because of this, care must be
taken when giving users access to commands via sudo to
verify that the command does not inadvertently give the user
an effective root shell. For more information, please see
the PREVENTING SHEL ESCAPES section in sudoers(4).
ENVIRONMENT
sudo utilizes the following environment variables:
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EDITOR Default editor to use in -e (sudoedit) mode
if VISUAL is not set
HOME In -s or -H mode (or if sudo was configured
with the --enable-shell-sets-home option),
set to homedir of the target user
PATH Set to a sane value if the securepath
sudoers option is set.
SHEL Used to determine shell to run with -s
option
SUDOPROMPT Used as the default password prompt
SUDOCOMAND Set to the command run by sudo
SUDOUSER Set to the login of the user who invoked
sudo
SUDOUID Set to the uid of the user who invoked sudo
SUDOGID Set to the gid of the user who invoked sudo
SUDOPS1 If set, PS1 will be set to its value
USER Set to the target user (root unless the -u
option is specified)
VISUAL Default editor to use in -e (sudoedit) mode
FILES
/etc/sudoers List of who can run what
/var/run/sudo Directory containing timestamps
EXAMPLES
Note: the following examples assume suitable sudoers(4)
entries.
To get a file listing of an unreadable directory:
$ sudo ls /usr/local/protected
To list the home directory of user yazza on a machine where
the file system holding ~yazza is not exported as root:
$ sudo -u yazza ls ~yazza
To edit the index.html file as user www:
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$ sudo -u www vi ~www/htdocs/index.html
To shutdown a machine:
$ sudo shutdown -r ]15 "quick reboot"
To make a usage listing of the directories in the /home
partition. Note that this runs the commands in a sub-shell
to make the cd and file redirection work.
$ sudo sh -c "cd /home ; du -s * sort -rn > USAGE"
SEE ALSO
grep(1), su(1), stat(2), passwd(4), sudoers(5), visudo(1m)
AUTHORS
Many people have worked on sudo over the years; this version
consists of code written primarily by:
Todd C. Miller
Chris Jepeway
See the HISTORY file in the sudo distribution or visit
http:/www.sudo.ws/sudo/history.html for a short history of
sudo.
CAVEATS
There is no easy way to prevent a user from gaining a root
shell if that user is allowed to run arbitrary commands via
sudo. Also, many programs (such as editors) allow the user
to run commands via shell escapes, thus avoiding sudo's
checks. However, on most systems it is possible to prevent
shell escapes with sudo's noexec functionality. See the
sudoers(4) manual for details.
It is not meaningful to run the cd command directly via
sudo, e.g.,
$ sudo cd /usr/local/protected
since when the command exits the parent process (your shell)
will still be the same. Please see the EXAMPLES section for
more information.
If users have sudo AL there is nothing to prevent them from
creating their own program that gives them a root shell
regardless of any '!' elements in the user specification.
Running shell scripts via sudo can expose the same kernel
bugs that make setuid shell scripts unsafe on some operating
systems (if your OS has a /dev/fd/ directory, setuid shell
scripts are generally safe).
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BUGS
If you feel you have found a bug in sudo, please submit a
bug report at http:/www.sudo.ws/sudo/bugs/
SUPORT
Limited free support is available via the sudo-users mailing
list, see http:/www.sudo.ws/mailman/listinfo/sudo-users to
subscribe or search the archives.
DISCLAIMER
sudo is provided ``AS IS'' and any express or implied
warranties, including, but not limited to, the implied
warranties of merchantability and fitness for a particular
purpose are disclaimed. See the LICENSE file distributed
with sudo or http:/www.sudo.ws/sudo/license.html for
complete details.
ATRIBUTES
See attributes(5) for descriptions of the following
attributes:
box; cbp-1 cbp-1 l l . ATRIBUTE TYPE ATRIBUTE VALUE =
Availability SUNWsudor, SUNWsudou = Interface
Stability Uncommitted
NOTES
sudo does not create audit(2) records; for a Role Based
administration solution that performs auditing of all
actions, please refer to rbac(5).
Source for sudo is available on http:/opensolaris.org.
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